The present invention relates to a covering for an opening provided in the ground and which can be covered by a removable cover or grating to give access to the opening and for which a bearing part is provided on the inside of a frame positioned in the ground. A retaining web is shaped on the cover or grating and is insertable into a recess having a hinge located on the inside of the frame.
Numerous different constructions for ground and floor opening coverings are known. Apart from the known constructions, in which the cover or grating is insertable in a bearing surface provided on the inside of the frame, constructions are also known in which the cover or grating is connected to the frame by a hinge means. Thus, the cover or grating is pivotable about an axis located in the frame, so that the cover or grating can more easily be brought into its opening position.
In a known construction (FR-A-2 548 254), an insert is inserted in a recess closed at three sides. Two curved guide slots are formed in the insert. The retaining web shaped onto the cover can be introduced into the slots. To achieve this, two circular pins are shaped onto the free end of the retaining web so as to form the axis of rotation of the cover, which project into the guide slots. In order that the insert cannot slip out of the recess on the opening of the cover, retaining lugs are provided on the insert, which engage in a depression provided in the recess, accompanied by elastic deformation of the insert. However, in order that a reliable holding and retaining action is achieved, a relatively high precision of dimensions of the insert and retaining lug, as well as the depressions in the frame recess are required, and this is not achievable without additional expenditure in the conventional production of the coverings by casting. In another known construction (U.S. Pat. No. 3 130 651), a rectangular cover is inserted in a rectangular frame. A retaining web is shaped onto the edge or rim of the cover. The web is provided on either side with a circular pivot pin. The pivot pins are inserted in guide grooves formed on the sides of a recess in the covering frame. Within the guide grooves, the pivot pins form a pivot axis about which the cover can be pivoted. However, the pivot pins can easily slip out of the guide grooves, if the cover is elastically deformed by the traffic travelling over it. The same applies in the case of a third known construction (GB-A-474250). In this construction the cover is triangular and the guide pins are located on the ends of one side of a triangle. Correspondingly, there are two recesses in the frame, in which in each case is formed a guide groove for receiving a pivot pin.
All known coverings with hinge-like means for pivoting the cover or grating make use of pivot pins, which are usually shaped onto the retaining web of the cover or grating, or in the recess. These pins can be relatively easily damaged. However, if they are kept small, they constitute parts which, on opening the cover and due to handling by the operator, can be highly stressed or strained.